Spectroscopic investigations are performed in the framework of production processes of gases and liquids, for gaining information on the course of the production or the resulting material or the amount of the material which has resulted to this point in time, in order, for example, to be able to evaluate the already transpired conversion of two educts. It is known to take samples from the process, or from process fluids, as the case may be, and either place these directly in a spectroscopic apparatus in a suitable sample cuvette and then analyze, wherein then the analytical results are evaluated in a PC, or, alternatively, a sample can be drawn and this sample is then connected with a spectrometer by means of a optical waveguide, so that no direct filling of the liquid into the spectrometer need occur.
Problematic in both of these known procedures is the sample taking, since this involves a not insignificant time factor, i.e., on the one hand, time and personnel are needed for the sample taking, and, on the other hand, for continuous processes, there is always a delay between getting the results of the spectroscopy and the taking of the sample. I.e., a direct following of the process and, in the end, its control and regulation by means of spectroscopy is not possible with such off-line measurements.
Additionally, there is associated with the sample taking, along with the disadvantage of only discontinuous measurement, always the possibility of an endangering of health, since the person taking the sample can possibly come into contact with the fluid being taken as the sample. There is also the possibility of contaminating the production stream.
Particularly when measuring using optical waveguides, which couple the light into the liquid and then transmit back to the spectrometer, there is the additional disadvantage that such light guiding connections can not be realized over arbitrarily long distances and also are not usable for all spectral regions.